The present application is a continuation of International Application No. PCT/SE99/01947, filed Oct. 28, 1999, which claims priority to Swedish Application No. 9902466-3, filed Jun. 24, 1999. Both applications are expressly incorporated herein by reference.
1. Technical Field
The present invention relates to an internal combustion engine and a method for operating a multi-stroke combustion engine provided with individually variable controlled inlet and outlet valves in each cylinder.
2. Background Information
Most current standard production car engines use a principle of operation known as four-stroke operation. These four strokes are referred to as the compression, expansion, exhaust and intake strokes. The principles of two-stroke operation and six-stroke operation are also known but restricted in their frequency of usage. An internal combustion engine that can operate under more than one stroke mode is defined as a multi-stroke engine. In U.S. Pat. No. 5,131,354, the two-, four- and six-stroke operation of an internal combustion engine is described. The six-stroke operation is described only in combination with engine start and warm-up.
In internal combustion engines, the decrease in combustion frequency reduces the maximum output, which can be described as the frequency of combustion times the maximum output per combustion. The maximum output per combustion is determined by the geometry of the engine.
A combination of multiple stroke operation modes can remove this restriction. However, previous considerations regarding the demand for high performance have prevented these more efficient engines with strokes greater than four from becoming more common. The complexity of the required system, which allows for a of a number of stroke operation modes, is extremely high. This complexity makes mass production not cost-effective or feasible.
The system complexity is due to the requirements a combustion cycle sets in combination with the degree of freedom required for multi-stroke operation. Implicit with multi-stroke operation is that changes between two or more stroke modes have to be performed. A smooth transition between two such stroke modes places a high demand on the degree of freedom of the system.
For non-transition between stroke modes, the following can be said. Normal combustion requires all valves in a specific cylinder where the combustion takes place to be closed during a certain part of the combustion. To achieve combustion with normal efficiency, the combustion should occur in the vicinity of top dead center (TDC), i.e., close to the crank angle degree where the piston in the specific cylinder reaches the highest position. These two criteria alone are not problematic in achieving. For a standard production engine, the camshaft and crankshaft are constructed so that this is guaranteed for four stroke operation. However, under multi-stroke operation, the interval or frequency of combustion changes. The change in frequency is a restriction posed by drivability criteria. A non-equidistantly fired engine shows a very unstable or undrivable character, especially at lower speeds and/or high loads. The combination of restrictions, ie., TDC and closed valves, for a combustion of equidistantly fired engine that is achieved for four-stroke operation also has to be met for these different intervals.
As with non-transition, a proper transition between stroke modes is also restricted in its possibilities, again considering the requirements of TDC and closed valves. An additional restriction in this case is the requirement of having an ignitable mixture in the cylinder at firing conditions. This implies that a number of cylinders are excluded from participation in this transition, since they either contain burned gas or have to be prepared for firing during the next cycle. This latter restriction prohibits fired operation, because this will have the implication that the next cycle has burned gas in the cylinder. Pressurized filling methods such as turbo charging, compressor charging and other methods, allow for exhaust and intake in only two strokes.
The present invention provides an internal combustion engine that overcomes the above-mentioned disadvantages of closed valves, TDC positioning and ignitable mixture, while providing a method for transition between different stroke modes throughout the entire operating range for an internal combustion engine.
The invention also increases the efficiency of the internal combustion engine, thereby reducing the fuel consumption of the engine. The present invention also an internal combustion engine with reduced emissions.
The internal combustion engine of the present invention operates by controlling the inlet and outlet valves so that the opening and closing of the valves are adapted to a second stroke mode that is different from a first stroke mode in which the engine currently running, controlling the injection of fuel into the cylinders so that fuel is injected prior to an expansion stroke, and transitioning from the first stroke mode to the second stroke mode independent of the operating condition of the engine throughout the entire operation of the engine.
Under constant conditions, i.e., constant power demand, an increase in work performed per combustion can be achieved by reducing the combustion frequency. The increased amount of work performed per combustion increases the efficiency, thereby reducing fuel consumption. However, since an internal combustion engine operates under different loads and speeds, it is essential that the transition between different stroke modes be performed independent of the operating condition of the engine throughout the entire operating range of the engine.
The previously described higher amount of performed work at a lower frequency, improves the combustion conditions in such a way that emissions are reduced under active catalyst conditions.
The present invention also provides a smooth and fast transition between the different stroke modes. This is accomplished by an internal combustion engine having individually and variably controlled inlet and outlet valves in each cylinder and a control device for controlling the ignition.
The control device is able to change the ignition order of the cylinders when the operation of the engine is converted from a first stroke mode to a second stroke mode. The changing of the ignition order leads to a smooth and fast transition between the different stroke modes. This implies that an extra degree of freedom in the system has to be present in order to achieve a transition with consideration for drivability.
With the introduction of electrically controlled valve mechanisms, such as hydraulically, pneumatic, electromagnetic and piezo-electrical, a possibility of adaptation for mass production of an engine that can be operated in a variety of stroke modes has arisen. The electronic control unit can meet the closed valve restriction independent of any engine state.